Metal–Ligand Role Reversal: Hydride-Transfer Catalysis by a Functional Phosphorus Ligand with a Spectator Metal

Hydride transfer catalysis is shown to be enabled by the nonspectator reactivity of a transition metal-bound low-symmetry tricoordinate phosphorus ligand. Complex 1·[Ru]⁺, comprising a nontrigonal phosphorus chelate (1, P(N(o-N(2-pyridyl)C₆H₄)₂) and an inert metal fragment ([Ru] = (Me₅C₅)Ru), reacts with NaBH₄ to give a metallohydridophosphorane (1^H·[Ru]) by P–H bond formation. Complex 1^H·[Ru] is revealed to be a potent hydride donor (ΔG°_H–,exp < 41 kcal/mol, ΔG°_H–,calc = 38 ± 2 kcal/mol in MeCN). Taken together, the reactivity of the 1·[Ru]⁺/1^H·[Ru] pair comprises a catalytic couple, enabling catalytic hydrodechlorination in which phosphorus is the sole reactive site of hydride transfer.